The present invention generally relates to a battery pack. More specifically, the present invention relates to a battery pack with batteries and an associated circuit and the like housed in an outer case thereof, such as a battery pack which houses secondary batteries such as lithium ion batteries.
As a portable power source for portable electronic devices such as notebook computers, digital cameras, or video cameras, a chargeable battery pack is used. As electronic devices have become highly efficient, downsized, and portable, research and development to enable the battery pack to operate for a long time is actively promoted. For example, a battery pack using lithium ion secondary batteries are of much interest, since it provides a larger energy density compared to conventional battery packs which use lead batteries or nickel-cadmium batteries, and it has little memory effect.
However, the lithium ion secondary battery is in danger of being destroyed due to overcharge and over discharge. Additionally, charge and discharge varies with respect to the individual battery. Therefore, particularly in the battery pack using a plurality of lithium ion secondary batteries, a circuit to uniform charge conditions by controlling charge and discharge for every individual battery, or a circuit to prevent over discharge and overcharge is connected in many cases. Such circuit is directly welded or soldered to the batteries by tabs made of, for example, nickel (Ni).
However, in the conventional battery pack wherein its batteries and its circuit are directly welded or soldered, when the lithium ion secondary batteries are destroyed due to over discharge or overcharge, there is the danger that an electrolytic solution made of an organic solvent leaks and contacts electronic parts of the circuit, leading to a major accident such as smoking and ignition due to migration. Additionally, there is a problem such that when a defect of the battery or the circuit individually occurs after assembly, a whole set of the batteries and the circuit is disposed, resulting in reduced manufacturing yield ratio and increased waste.
The batteries are generally consumed earlier than the circuit in the battery pack in many cases. However, when trying to replace only the battery after it is consumed, in reality, it is impossible to remove the tab from the consumed battery and mount a new battery since the battery and the tab are spot-welded. Therefore, when the battery is consumed, a whole set of the batteries, tabs, and the circuit has to be disposed in spite of no deterioration in the circuit. This causes a problem in terms of environmental aspect, resource conservation, or effective use of resources as well.